JPH0569545B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to new and improved thin, soft absorbent products, and more particularly, to incorporate superabsorbent materials and absorb large amounts of liquid. Relating to a new and improved soft compressed composite. Disposable products have been known for some time, including disposable diapers, wound dressings, bandages, incontinence pads, and the like. These products incorporate absorbent vats that are used to absorb and retain or contain body fluids. First, in many of these products, especially disposable diapers and sanitary napkins, the absorbent butt is constructed from what is referred to as "wadding" or tissue ply. The batting was placed between the liquid-impermeable backing sheet and the liquid-permeable facing sheet, and the Teitshu ply was used to absorb and preferably contain liquid within the product. A diaper utilizing such an absorbent batt is disclosed in US Reissue No. 26151. Wadding-type products have been replaced by improved absorbent batts made of what is commonly referred to as "fuzzy wood pulp fibers." This absorbent vat consists of a layer of individualized wood pulp fibers,
This layer has a substantial thickness. A diaper incorporating such fuzzy wood pulp fibers is described in US Pat. No. 2,788,003. This diaper has improved absorbent capacity and somewhat better containment than diapers that use a batting layer. The fuzzy wood pulp layer is also very soft, pliable, and comfortable, thus producing an improved diaper over diapers that use cotton batting as the absorbent layer. Although fuzzy wood pulp absorbent vats have improved capacity, the efficiency when using that capacity in diapers or sanitary napkins is low. The reason for this is that the fluid to be absorbed is generally located in localized areas within the absorption vat and the ability to remove fluid along the plane of the vat is poor. The fluid flows through the path of least resistance and eventually moves to the nearest edge of the vat where it is no longer contained and leaks product. Additionally, wood pulp batts lack stability; for example, when a diaper is being worn, the batts tend to break and clump. US Pat. No. 3,017,304 discloses an absorbent product that incorporates a densified paper-like layer in the product.
This paper-like layer acts as a wicking layer, and liquids placed on the layer tend to move rapidly along the plane of the layer. When combined with fluffed wood pulp fibers, the resulting product uses the absorbent capacity of fluffed wood pulp very efficiently. Diapers incorporating this paper-like layer in combination with fluffed wood pulp are disclosed and described in US Pat. No. 3,612,055 and US Pat. No. 3,938,522. The concept of combining a wicking or capillary skin or layer with fuzzy wood pulp fibers is widely accepted in many absorbent products, including disposable diapers and sanitary napkins. These products greatly increase the use of the capacity of the absorbent vat, but do not completely contain the absorbed liquid. These products can leak before the entire capacity of the vat is used for absorption.
This is especially true when pressure is applied to the diaper while the vat is wet; for example, if an infant sits on a pre-wet diaper, the vat may leak. Although the vat is somewhat stabilized by a paper-like densified skin, it can crack and separate. Recently, elastic leg diapers or stretch diapers have become available on the market. Although these diapers did not provide superior absorbency than flat diapers or prior art diapers, they did exhibit improved fluid retention. Such diapers are covered by U.S. Patent No.
No. 3860003, No. 4050462 and No. 4324245. Although this containment feature is superior to prior art products, the elastified product fits more tightly and allows for less air circulation. Frequently, this can become irritating to the skin, and the tighter the elastic, or the more tightly fitted the diaper, the greater the irritation. this is,
This is especially true in areas where the elastic legs of the product come into contact with the wearer. A few years ago, ``superabsorbent materials'' were developed that can absorb many times their weight in liquid. Attempts have been made to develop such materials and incorporate them into absorbent products such as diapers and sanitary napkins to increase the absorbent performance of these products. In theory, a minimal amount of superabsorbent incorporated into a product would cause the product to perform as well or better than prior art products. Perhaps one of the first products to incorporate such superabsorbent materials in a disposable diaper is disclosed in US Pat. No. 3,670,731. This patent discloses an absorbent dressing consisting of an absorbent layer sandwiched between a sheet of permeable facing material and a sheet of impermeable facing material. This absorbent layer contains water-insoluble cross-linked hydrocolloids as superabsorbent substances. Although superabsorbent materials have been available for some time, they have not gained wide acceptance in absorbent products such as disposable diapers and sanitary napkins.
The main reason for this is the failure to develop products that can economically exploit the highly increased absorption capacity of superabsorbent materials. In order to utilize superabsorbent materials economically, the liquid to be absorbed must be transferred to the superabsorbent material. As a maxim, superabsorbent materials must be placed in contact with liquids. Furthermore, when the superabsorbent material absorbs liquid, it must be able to swell. When superabsorbent materials are prevented from swelling, they stop absorbing liquids. Therefore, the structure of the absorbent layer containing superabsorbent substances appears to be important if it is to function in diapers and sanitary napkins where the liquid to be absorbed is located in small void areas. Over the years, a number of techniques have been disclosed in an attempt to efficiently use superabsorbent materials. Such products are disclosed in US Pat. No. 4,103,062, US Pat. No. 4,102,340 and US Pat. No. 4,235,237. Additionally, methods of incorporating superabsorbent materials in suitable layers or suitable steric configurations that can be placed in absorbent products are described in U.S. Pat. No. 4,186,165;
No. 4340057 and No. 4364992. To date, none of these products have achieved substantial commercial success. Co-pending Application No. filed November 8, 1982
A particularly useful compressed composite is formed in No. 439,963. This application is incorporated herein by reference. This compressed composite product is preferably made from a nonwoven fabric such as polyester. The fabric foil has associated therewith at least 200% by weight of superabsorbent material to form an absorbent layer. To provide a product that not only absorbs liquid, but also transports liquid, wood pulp fibers or other suitable wicking materials are cast in a layer on at least one side of the absorbent layer. The product is then compressed to produce a highly liquid absorbent product.
However, the resulting compressed composite is very stiff and therefore needs to be softened to provide flexibility for use in products such as diapers and the like. The flexibility provided needs to be permanent, ie the surrounding environment, handling of the product and its subsequent use will not affect the softness and flexibility. The present invention provides a new and improved absorbent structure that utilizes a substantial portion of the absorbent capacity of superabsorbent materials and is soft and pliable. This soft, pliable composite is substantially completely stable and retains its stable state even though it is soft and pliable. Whether wet or dry, the complex does not break down, clump, or separate. This soft composite, when under pressure, retains the absorbed liquid without leaking it. The present invention provides an absorbent composite product structure constructed from a fibrous web, a superabsorbent material, and other materials suitable for wicking liquids. The fibrous web contains superabsorbent material disposed in the fibers of the web in an amount of at least 200% by weight, based on its weight. A wicking layer is formed from a suitable wicking material, such as wood pulp fibers, and placed over the fibrous web, and the two layers are compressed to produce a compressed composite structure. Absorbent composite structures are considered flexible and have a Taber stiffness value of approximately 25 or less.
stiffness value). The fibrous web used as the basis for the absorbent layer of the compressed composite structure is preferably a low-density elastic fibrous web of randomly arranged fibers with a dry bulk recovery rate of at least 30%.
recovery) and an initial dry bulk of at least 20 c.c./g, a wet bulk of at least 30 c.c./g, and about 135.62 g/cm ² (4
ounces per square yard), preferably
This results in a web having a weight of ^less than 3 ounces per square yard. The fiber web is
It is used to spatially distribute the superabsorbent material so that when exposed to an aqueous liquid, swelling occurs with minimal interference from adjacent superabsorbent materials. After formation of the absorbent layer, the wicking layer is formed as a superimposed layer on the absorbent layer. The wicking layer is generally a layer of wood pulp fibers in an amount of about 4 ounces per square ^yard or more. These two
The layers, while still in a wet state of at least about 10% moisture, are compressed to form a compressed composite product. The resulting compressed composite product is too stiff for most applications due to the high loading of superabsorbent material in the absorbent layer. It has been discovered that this compressed composite product can be softened to a Taber stiffness value of about 25 or less. The present invention further provides a method of manufacturing absorbent composite structures that are soft and pliable. The compacted composite product described above is first subjected to microcorrugating and then perf-embossing. The microcorrugation process consists of passing the web through interlocking fluted rolls with sufficient pressure to fracture the superabsorbent material and form transverse hinge lines. Here, perf embossing refers to forming a composite structure into upper and lower parts in which the upper roll and the lower roll each have an interlocking knuckle.
passing between a pair of rolls, which thereby forms a raised area and a recessed area in the composite structure;
means. Perf embossing is covered by U.S. Patent No.
No. 3,817,827. In order to soften the absorbent composite structure and substantially reduce the Taber stiffness,
It is necessary to bring the superabsorbent material to its glass transition temperature so that the superabsorbent polymer becomes brittle and can be effectively reduced in size by mechanical processing and fracturing provided by microcorrugation and perf embossing. It is. The glass transition temperature is reached by reducing the moisture sufficiently to allow satisfactory operation at the temperature of the room in which the operation is being performed. For most superabsorbents,
A satisfactory moisture content is less than about 10% by weight of the absorbent composite structure. In the process of microcorrugation, the Taber stiffness is reduced by at least 50%, and often by at least 70%. During the subsequent perf embossing process, the Taber stiffness value is generally less than 15;
In each case it is reduced to a value less than 25. Perf embossing should provide sufficient impact points to the product to further reduce the particle size of the superabsorbent polymer. Generally, satisfactory changes in Taber stiffness values will be achieved when the points of impact are less than 1/4 inch apart and more or less continuous. In the perf embossing method, the complex is 1
It is passed through a pair of rollers. These rollers have knuckles and interlock to shear the composite structure in the desired manner. When the structure is viewed after perf embossing, there is a raised area created by the lower knuckle and a recessed area created by the upper knuckle. When the structure is viewed from the other side, the raised areas become recessed and the recessed areas become raised areas. The depression is a densification area that holds and wicks liquid. The area interconnecting the raised areas and the depressions is the middle part in the area that has undergone most of the machining that reduces the size of the superabsorbent polymer and melts the layers of the composite in the shear area. At locations where the top knuckle of the roll passes very closely to the bottom knuckle, the work applied to this structure overpowers the structure and creates an aperture therein. The length of the opening can be varied by adjusting the overlap of the upper and lower knuckles of the roll or the size of the knuckles. The flexibility of the structure is increased by the apertures, which can reduce the overall strength of the product. Accordingly, preferred products of the invention employ controlled areas of both apertures and partially fractured or sheared areas. Referring to the drawings, FIG. 1 is a perspective view of the starting material used to make the compressed composite product that is softened in the present invention. The starting material 10 is a fibrous web 12, which comprises at least 200% of the web.
Contains % superabsorbent material. Superabsorbent material 16 is distributed throughout fibrous web 12 . Wicking layer 1
4 are arranged on each side of the fibrous web 12. The wicking layer is generally wood pulp fiber. When the product is compressed, the transition zone 18 is located at the junction on each side of the absorbent layer, i.e. the fibrous web 12 and the wicking layer 1.
4 is formed at the junction with 4. FIG. 2 shows a section of the product of FIG. 1 with a fibrous web as absorbent layer 22. FIG. A superabsorbent material 24 is interdispersed between the fibers of the absorbent layer. The wicking layer 28 is immediately associated with the absorbent layer. Some portions of the wicking layer fibers 26 extend into the absorbent layer 22 and become integrated therewith. In this way, a transition zone 25 is formed. "Integral web" means in intimate contact but without requiring physical or chemical bonding. Second
The structure shown in Figure A is the compressed version of Figure 2. Upon compression, some of the portions of the wicking layer 28 extend into the absorbent layer 22 and become integrated with the fibers of the absorbent layer 22. Portions of these wicking layers are also in contact with the superabsorbent material 24. When compressing the structure and giving rise to a softened surface of the superabsorbent material to provide the necessary contact to the fibers of the absorbent layer so that the composite remains compressed even when dry , generally at least 10% moisture is present. FIG. 3 is a perspective view of the absorbent composite structure of the present invention, ie, the microcorrugated structure of FIG. 2A. The structure 30 includes a wicking layer 32, an absorbent layer 34, and micro-corrugated hinge lines 36 and 38 that provide a Taber stiffness of about 25 or less. FIG. 4 is a perspective view of an absorbent composite structure perf embossed according to the present invention after microcorrugation. The composite 40 has a wicking layer 44 and an absorbent layer 42. After microcorrugation and perf embossing, hinge lines 46 and apertures 49 are arranged in the structure to provide the pattern shown. The Taber stiffness of this product is at least 75% less than that of the product before treatment and in most cases less than 15. FIG. 5 shows a disposable diaper 50 that utilizes the absorbent composite structure of the present invention. Portions of the drawing have been destroyed for clarity. disposable diaper 5
0 has a liquid permeable face material 56 and a liquid impermeable back material 52. An absorbent composite structure 54 is present between the facing material 56 and the backing material 52. Diaper 50 is laminated into a unitary configuration by lines 58 of absorbent material. It has tape tabs 59 for securing the diaper product 50 around the waist of the wearer. FIG. 6 is a perspective view of the sanitary napkin 60. The napkin is comprised of a liquid-impermeable outer shell 64 containing an absorbent composite structure 66 and covered over its upper surface with a liquid-permeable facing material 62. Absorbent structure 66 is made in accordance with the present invention and is similar to that of FIG. 7 is an enlarged side view of a portion of the embodiment shown in FIG. 3; FIG. Portion 70 is comprised of an absorbent layer 74 and a wicking layer 72. The microcorrugation provides the hinge line 76. FIG. 8 is an enlarged side view of a portion of microcorrugation rolls 82 and 84. The roll has interdigitating flutes 86 and 88. These flutes provide the hinge lines mentioned above. FIG. 9 is a graph showing test results of Examples. The tests performed on control samples and samples made according to the invention are derived from the GAT apparatus described and disclosed in US Pat. No. 4,357,827, issued November 9, 1982. The values given represent the absorbency of urine solution simulated under 0.5 psi at different times. The absorbency value is what the structure can absorb for a given amount of time while under a load of 0.5 psi.
The values given in FIG. 9 will be considered in the examples. The products shown in the drawings and other products, e.g.
Incontinence pads, wound dressings, etc. can be made from the absorbent composite structures of the present invention. FIGS. 10 and 11 show an example of an apparatus for performing perf embossing. Referring to FIGS. 10 and 11, the composite structure 110 includes a pair of cylindrical embossing rolls 111.
and 112 to produce a perf-embossed structure 113. Embossing rolls 111 and 112 have knuckles 114 and 115, respectively, which interlock to deform the composite structure into the desired shape. FIG. 8 shows an upper knuckle 114 and a lower knuckle 1.
Fifteen relative positions are shown. A composite structure perf embossed with the above-mentioned knuckles is shown in FIG. The lower knuckle creates a raised region 116 in the composite structure, and the upper knuckle creates a recessed region 117. Of course, when the composite structure is viewed from below, the protruding region 116 becomes a recessed region, and the recessed region 11
7 becomes a protruding area. At the junction of the protruding region 116 and the recessed region 117 an intermediate portion 118 occurs. This intermediate portion 118 is subject to the strongest mechanical action;
Causes partial destruction of the structure. Upper nutcle 11
At locations 19 where 4 is very close to the lower knuckle 115, the action on the composite structure may be greater than the strength of the structure, creating an opening 120 in the structure. The fibrous web containing superabsorbent and forming the base layer for the absorbent composite structure of the present invention has a substantially high loft and is dry compacted and
When it is then opened, it has a tendency to return to substantially its original thickness. For example, synthetic staple fibers,
For example, fibrous webs formed from polyethylene, polypropylene, polyester, nylon, bicomponent fibers, and the like are particularly desirable. Melt spun webs are also suitable. Generally, the fibers are air laid or melt blown to form a web;
This web is stabilized if necessary. Stabilization is done by heat-through bonding,
This can be accomplished by adhesive bonding, point embossing using heat or adhesive, and the like. The stabilization method is chosen according to the fibers and method used to form the web. Suitable procedures for forming the web include carding, wet laying, air laying, or a combination thereof;
Including melt blow molding and other suitable known techniques. The fibrous web preferably has at least about
30% dry volume recovery and at least 20 c.c./g
and a wet volume of at least 30 c.c./g. Fibrous webs generally have approximately
It has a weight of less than 4 ounces per square ^yard , preferably less than about 3 ounces per square ^yard . Generally a wicking layer of wood pulp fibers is disposed on at least one side of the superabsorbent-containing fibrous web;
And compress this product in the presence of moisture of about 10% or more. The resulting compacted composite generally has a diameter in the machine direction of at least 130, sometimes
It has a high Taber stiffness of around 350. The superabsorbent material present in discontinuously dispersed form in the absorbent layer is a water-swellable polymeric material that is generally water-insoluble but capable of absorbing water in an amount at least 10 times the weight of said material in its dry form. It is. Superabsorbent materials are fibers, spheres, film bits,
It can be applied in the form of particles, which can be in the shape of globules or the like, or in the form of a liquid monomer solution that can be subsequently polymerized. Generally, the polymerized monomer solution provides bits of globule and film-like particles in the structure. In one type of superabsorbent material, the particles or fibers have a backbone of a natural or synthetic polymer with hydrophilic groups, or polymers containing hydrophilic groups chemically bonded to the backbone. Can be described chemically as a homogeneous mixture. This class of materials includes: modified natural and regenerated polymers, for example modified to be highly hydrophilic by carboxylation, phosphonoalkylation, sulfoalkylation or phosphorylation; Polysaccharides such as cellulose and starch and regenerated cellulose. Such modified polymers can be crosslinked to improve water insolubility. These same polysaccharides can also serve as backbones onto which other polymer moieties can be attached, for example, by graft copolymerization techniques. These grafted polysaccharides and methods for their production are described by Chatterjee.
No. 4,105,033 to et al. and can be described as a polysaccharide chain having a hydrophilic chain grafted thereon of the following general formula:

[ka]

[Chemical formula] Wherein A and B are selected from the group consisting of -OR ³ , -O (alkali metal), -OHNH ₃ , -NH ₂ ,
R ¹ , R ² and R ³ are selected from the group consisting of hydrogen and alkyl having 1 to 4 or more carbon atoms, r is an integer having a value of 0 to about 5000 or more, and s is 0 to about 5000. r+s is at least 500, p is an integer having a value of 0 or 1, and q is an integer between 1 and 4.
is an integer with value . Preferred hydrophilic chains are hydrolyzed polyacrylonitrile chains and copolymers of acrylamide and sodium polyacrylate. In addition to modified natural and recycled polymers,
The hydrocolloid particle component can constitute a completely synthetic hydrophilic particle. Examples of what is currently known in this field are: polyalrylonitrile fibers that can be modified by grafting moieties such as polyvinyl alcohol chains, polyvinyl alcohol itself, hydrophilic polyurethanes. , poly(alkylphosphonates), partially hydrolyzed polyacrylamides [e.g., poly(N,N-dimethylacrylamide), sulfonated polystyrene, or poly(alkylene oxide) classes]. These highly hydrophilic synthetic polymers can be modified by other chemical treatments, such as crosslinking or hydrolysis. Other examples known in the art are nonionic hydrophilic polymers, such as polyoxyethylene, polyoxypropylene or mixtures thereof, suitably cross-linked chemically or by radiation. Other more recent types include
It is a derivative of isobutylene-maleic anhydride copolymer. A hydrophilic polymer formed from a water-soluble acrylate monomer, such as a salt of sodium, potassium, or ammonium (or a combination of these cations) of acrylic acid, is deposited onto the absorbent layer by spraying or otherwise applied to the solution. It can be placed thereon and then polymerized and crosslinked, for example by irradiation. In addition, naturally occurring substances, general formulas, rubbers can be used. For example, guar gum is suitable. The superabsorbent material is combined with the fibrous web by suitable means so as to minimize the interference of one superabsorbent entity with the other during its swelling. Blows out absorbing substances. When the superabsorbent material is a powder, it can be sprinkled in dry form onto the fibrous web, or the web can be moistened. When the superabsorbent material is in granules, it may be desirable to slightly moisten it before contacting it with the web. Superabsorbent material has a diameter of 0.005
Contains particles ranging in size from mm to globules;
It may be continuous for up to several inches along the fiber. Other methods of placing the superabsorbent in the web are by spraying the monomer solution onto the web or by saturating the web with the monomer solution and then polymerizing the monomer. One typical method of polymerizing monomers is to polymerize the monomers by irradiation. It is desirable to distribute the superabsorbent more or less uniformly throughout the fibrous web. However, even when the superabsorbent is powder-like and in the form of a layer, it tends to perform better than such layers in previously known products. It may be desirable to have more superabsorbent in some areas than in other areas and/or in a predetermined pattern within the superabsorbent structure. Any superabsorbent that absorbs large amounts of liquid is suitable for use in the absorbent layer of the present invention. As previously mentioned, compressed composite products containing superabsorbents tend to be stiff and substantially inflexible. Because fiber end uses require the web to be soft, pliable, and pliable, microcorrugation and perf embossing can meet the stiffness requirements without damaging the composite properties desirable for that end use. It was discovered that it provides a reduction. Often, the Taber stiffness of composites in which the absorbent layer contains at least 200% superabsorbent exceeds a Taber stiffness value of 300 in the machine direction. In the lateral direction, the Taber stiffness is generally greater than 70.
To obtain a product satisfactory for use in disposable products such as diapers and sanitary napkins, the Taber stiffness value should be approximately
25, preferably below 15. Taber stiffness values were obtained according to the procedure described in ASTMD 2969 and g/diameter
Expressed in cm. The wicking layer is constructed of hydrophilic fibers, such as rayon fibers, cellulose, peat moss, acrylic fibers, or mixtures thereof. Cellulose fibers include wood pulp fibers, cotton linters, and the like. Wood pulp fibers are commonly used to form the fluff or fiber batts in conventional absorbent products, such as disposable diapers, sanitary napkins, and the like. Other cellulose fibers that can be used are rayon fiber, flax, hemp,
There are jute, ramie, cotton, and cotton lintern.
Fiber or peat moss or mixtures thereof
The particles are arranged in such a way that they are in close contact with each other so as to provide higher capillary pressure to facilitate liquid wicking in the plane of the layer. What appears to be only a small difference in capillary pressure is all that is required of one layer to draw in and expel liquid from an adjacent layer. The force that causes liquid to enter the cylindrical capillary is
It is expressed by the following equation: P=(2υ cos θ)/r where the force is expressed by the capillary pressure and P
is the capillary pressure, υ is the liquid surface tension, θ is the liquid-fiber contact angle, and r is the capillary radius. For a given liquid, the pressure (capillary force) increases with the cosine of the liquid-fiber contact angle (reaching a maximum when the angle is 0) and also increases with decreasing capillary radius, so that thinner capillaries It will draw more liquid than a thicker capillary. The suction between the first fibrous layer and the second layer is influenced by both the relative density of the layers and the relative wettability of the individual fibers in each layer. The individual fibers of the second layer preferably have liquid fiber contact angles that are substantially smaller than those of the first fiber layer to overcome the density difference and significantly increase the overall capillary pressure. The liquid is absorbed into the second layer. The fibers of the second layer of fibers (or particles) and/or the density of that layer are selected to create a significant difference in capillary pressure from the first fiber layer. The second fiber (particle) layer is generally composed of fibers that have a lower liquid-contact angle or the layer has a narrower capillary radius. Examples of such fibers include hydrophilic fibers such as rayon fibers, cellulose fibers, or peat moss, or mixtures thereof. Cellulose fibers include wood pulp fibers, cotton linters, and the like. The wicking layer may be preformed and placed adjacent to the absorbent layer prior to compression, or the particles of the wicking layer may be air laid onto the absorbent layer prior to compression, mechanically intertwined therewith, or wet laid. be able to. The transition zone is the area that forms at the junction of the absorbent layer and the wicking layer. Some of the particles of the wicking layer, for example fibers, extend into the absorbent layer and become integrated therewith. The area where most of the extending particles lie is identified as the transition zone. In the transition zone there is a composite of absorbent layer fibers, superabsorbent material and wicking layer particles.
The particles of the wicking layer that extend into the absorbent layer are in intimate contact with a portion of the superabsorbent material of the absorbent layer.
This allows the liquid to start its movement in the z-direction and reach the superabsorbent material. As the liquid progresses in the z-direction, the superabsorbent material softens and releases the fibers of the absorbent layer, thus allowing the absorbent layer to return substantially above its uncompressed thickness. As the absorbent layer returns to its uncompressed thickness, a larger void area is formed which stores liquid and as the superabsorbent material absorbs the liquid present in the void area, an increase in the superabsorbent material occurs. This allows for swelling. The absorbent layer tends to return above its uncompressed thickness. This is probably due to both the elasticity of the fibers and the swelling of the superabsorbent material. In order to provide the necessary medium for the fibrous web of the absorbent layer to absorb liquid, the fibrous web has an initial dry volume of at least about 20 c.c./g, at least
a dry volume recovery rate of 30% (preferably 50%), a wet volume of at least about 30 c.c./g, and about
It preferably has a weight of 4 ounces per square ^yard . The initial dry volume is the area x thickness of the layer under a load of 0.01 psi, calculated in cubic centimeters. Divide this value by the weight (g) to obtain a measurement in cubic centimeters/gram. Dry volume recovery was determined by applying a 1.75 psi load to the web for 5 minutes, removing the load, and
This is obtained by allowing the web to stand for 1 minute, applying a 0.01 psi load to the web for 1 minute, and then measuring the final dry volume while under the 0.01 psi load. Dry volume recovery is expressed as a percentage of the final volume divided by the initial volume. Wet volume is measured in the same manner as initial dry volume, except the web is saturated with water. The fibrous web has a dry volume recovery rate of at least 20% (preferably 50%), at least 40%
cc/g, a wet volume of at least 30 c.c./g, and a weight of less than 135.62 g/cm ² (4 oz/sq yd), the fibrous web will contain at least 1500% of its dry weight. It was discovered that superabsorbent substances can hold up to The web is 200% of the dry basis weight of the web on a dry basis.
It is preferred to contain ~1500% superabsorbent material, and a range of about 400% to about 1200% is most preferred. The means for making absorbent composite structures flexible, supple and soft in accordance with the present invention is through one or more mechanical processing procedures. Preferred means of mechanical processing are microcorrugation and perf embossing. Microcorrugation techniques are described in US Pat. No. 4,116,892 to Shwarz. Although the technique in this patent is identified as stretching the fibers to orient them,
The present invention is intended for mechanical processing without stretching. Shwarz uses his technique to molecularly orient the fibers after they are in the molten state. Thus, additional stretching or further orientation can damage the fibers of the present invention. It has been discovered that microcorrugation of the absorbent structure defined in this invention provides hinge lines and produces a flexible, pliable, soft feel. 0.064 roll as described in U.S. Patent No. 4,116,892
~0.762cm (0.025~0.30 inch)
The superabsorbent particles are broken into more or less uniform sizes and the desired hinge lines described above are created. If the absorbent composite structure of the present invention is simply passed through a roll to break the structure, the product is actually stiffer and has a higher Taber stiffness value. The stretch on the fibers of the absorbent structure is less than 10% when performing microcorrugation. It is easiest to pass the compressed composite product through micro-corrugated rolls in the machine direction, and therefore it is the most desirable direction. However, microcorrugation in the machine direction, thereby placing the hinge line in the product in the machine direction, is acceptable. This can be accomplished using a roll with embossing rings arranged to provide the necessary hinge lines. It has been found that it is highly desirable to reduce the moisture content of the absorbent composite structure by less than 10% prior to microcorrugation. When the microcorrugated absorbent composite structure is microcorrugated and then subjected to perf embossing, the absorbent product is a flexible, pliable, and soft product that substantially follows its original machine direction. while retaining the strength of the material, improving absorption and reducing the Taber stiffness by a significant amount, such that the final Taber stiffness is below 25, preferably below 15.
It was discovered that it can be machined. Perfume embossing is a known technique, e.g.
It is implemented by the technique exemplified in No. 3,817,827. In order for the composite to be best processed, the superabsorbent polymer must be brittle and effectively reduced in size by the mechanical processing and shear provided by perf embossing.
It is preferred to obtain the glass transition temperature of the superabsorbent material. The glass transition temperature is reached by reducing the moisture sufficiently to allow satisfactory operation at the temperature of the chamber in which the operation is being carried out. For most superabsorbent materials, a satisfactory moisture content is less than about 10% by weight of the composite structure. In addition to the soft, pliable, improved flexibility of the absorbent composite structure, the product was observed to absorb liquids in greater amounts than before mechanical processing procedures. Furthermore, the rapid absorption of the form by the product is not substantially reduced. Quality is particularly beneficial for compressed composite products used in disposable diapers. The method of making compressed composites of the present invention is illustrated by the following examples. EXAMPLE An absorbent layer for a compressed composite is formed from 67% polyester fibers and 33% bicomponent fibers.
Bicomponent fibers have a polyethylene sheath and a polyester core. The webs are thermally bonded by passing 177°C (350°C) air through the webs for about 1 second or less. The obtained web is 40.69g/m ²
(1.2 ounces/square yard). The web is coated by flooding the web with an aqueous solution of sodium acrylate and acrylic acid. Excess solution is removed from the web and the web is then exposed to electron beam radiation. This electron beam radiation polymerizes the sodium acrylate to sodium polyacrylate. The web is repeatedly flooded with liquid and exposed to radiation each time to achieve a dry solid coverage of sodium polyacrylate of 10 times the weight of the web. The polyacrylic acid coated web is passed under a hammer mill which deposits the wood pulp fibers onto the polyester web. Vacuum pressure is applied below the polyester web to cause the wood pulp fibers to be lightly compressed onto the web. Wood pulp fiber is approx.
A layer of wood pulp fibers is present in an amount of 4 ounces/square yard (135.62 g/cm ² )/layer and is deposited on each side of the polyester web. The surface of the pulp layer is sprayed with water, thereby bringing the total moisture content of the pulp to at least 10% by weight. The entire structure is then compressed to a level of 640 psi for 30 seconds. Upon release of the pressure, the pulp forms into a dense layer, which has capillary dimensions suitable for liquid wicking, and the elastic fiber layer is in a compressed state. A product containing about 20% moisture has a Taber stiffness of about 343 in the machine direction and 75 in the transverse direction. compression complex
When subjected to perf embossing at 20% moisture, the Taber stiffness in the machine direction increases to approximately 376;
On the other hand, the lateral Taber stiffness value decreases slightly to a value of approximately 65. In all cases, Taber stiffness values are expressed in grams per linear cm of sample. A compressed composite product containing approximately 20% moisture is
% moisture and microcorrugated in the machine direction. The roll is 30dp [diametral pitch]
pitch)] has a minute waveforming peak.
It is a 17.78 cm (7 inch) cylinder and the engagement is 0.102 cm (0.04 inch) at a pressure of 51.79 Kg/linear cm (290 pounds/linear inch). These samples have Taber stiffness values of approximately 27 in the machine direction and 15 in the transverse direction after microcorrugation. The sample is then subjected to perf embossing,
Here the roller is 0.127cm with 40psi engagement
(0.05 inch). The Taber stiffness of the microcorrugated and perf-embossed product is reduced to 8.0 in the machine direction and 3.6 in the transverse direction. It can clearly be seen that the stiffness in this product has been reduced by at least 75% in each direction. The mechanically processed product exhibits improved absorbency in exhibiting a 32% increase in absorbency after being mechanically processed. The absorbency results at given times are shown in graphical form in FIG. As can be readily appreciated, microcorrugation and perf embossing treated (MC/PE) samples absorb liquid much more rapidly than untreated compacted composite products over a given period of time.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of one type of starting material of the invention. FIG. 2 is an enlarged cross-sectional view of FIG. 1 taken along line 2--2. FIG. 2A is a cross-sectional view as in FIG. 2 after compression of the product.
FIG. 3 is a perspective view of the product after the micro-corrugation process. FIG. 4 is a perspective view of one embodiment of the invention. FIG. 5 is a perspective view of one embodiment of the invention, partially broken away for clarity. FIG. 6 is a perspective view of another embodiment of the invention, partially exploded for clarity. 7 is an enlarged side view of a portion of the embodiment shown in FIG. 3; FIG. FIG. 8 is an enlarged side view of a portion of the micro-corrugating roll. FIG. 9 is a graph showing test results of Examples. FIG. 10 is a sectional view showing an example of an apparatus for performing perf embossing. FIG. 11 is a plan view seen from the direction of arrow 11 in FIG. 10. FIG. 12 is a perspective view of a composite structure perf embossed using the apparatus of FIGS. 10 and 11;

Claims (1)

Claims: 1. An absorbent layer comprised of a fibrous web, said web having an initial dry volume of at least about 20 c.c./g, a dry volume recovery of at least about 30%, and a dry volume recovery of at least about 30%.
cc/g wet volume and a weight less than about 135.62 g/cm ² (4 oz/sq yd) and containing at least 200% by weight absorbent and consisting of a wicking layer and less than about 25 A microcorrugated perf-embossed absorbent composite structure characterized by having a small Taber stiffness value. 2. The structure of claim 1, wherein the superabsorbent is present in an amount of about 200% to about 1500%. 3. The structure of claim 2, wherein the superabsorbent is present in an amount of about 400% to about 1200%. 4. The structure according to claim 1, wherein the fibrous web is a nonwoven polyester web. 5. The structure of claim 1, wherein the wicking layer is comprised of wood pulp fibers. 6. The structure of claim 1, wherein the Taber stiffness value is less than about 10. 7 having an absorbent core comprised of a microcorrugated perf embossed composite structure, said composite having an absorbent layer comprised of a fibrous web, said web having an initial dry volume,
dry volume recovery of at least about 30%, wet volume of at least about 30 c.c./g and about 13562 g/cm ² (400
ounces per square yard) and contains at least 200% by weight superabsorbent;
and a wicking layer, and having a Taber Stiffness value of less than about 25. 8. an absorbent core composed of a micro-corrugated and perf-embossed composite structure, the composite structure comprising an absorbent layer composed of a fibrous web;
The web has an initial dry volume of at least about 20 c.c./g, a dry volume recovery of at least about 30%, a wet volume of at least about 30 c.c./g, and about 13562 g/cm ²
(400 ounces per square yard) and containing at least 200% by weight superabsorbent, and comprising a wicking layer and having a Taber Stiffness value of less than about 25. Napkins. 9 Drying an absorbent composite structure consisting of an absorbent layer and a wicking layer composed of a fibrous web containing at least 200% by weight superabsorbent to a moisture content of less than about 10%, and drying the dried structure to a moisture content of less than about 10%. an absorbent layer comprised of a fibrous web characterized by microcorrugation and then perf-embossing to reduce the Taber stiffness value to less than 25, said web having an initial dry volume of at least about 20 c.c./g; Dry volume recovery rate of at least about 30%, at least about 30
cc/g wet volume and weight less than about 135.62 g/cm ² (4 oz/sq yd) and containing at least 200% by weight superabsorbent and consisting of a wicking layer and about 25% by weight superabsorbent; A method of manufacturing flexible, soft, absorbent composite structures with lower Taber stiffness values. 10. The method of claim 9, wherein the Taber stiffness value is reduced to about 10 or less.